1. Field of the Invention
The present invention relates to a sheet information output apparatus for gaining information as to a sheet material such as a paper sheet or a resin sheet by applying external force to the sheet material to detect a pressing force (impact force) through the sheet material. The present invention also relates to a sheet information output apparatus, a sheet processing apparatus and an image forming apparatus for conducting the prescribed output processing on the basis of gained information.
2. Description of the Related Art
In recent years, research and development on sheet processing apparatus and image forming apparatus for automatically distinguishing the kind of a sheet to be processed to adjust processing conditions have been progressed. Attending on this progress, there have been proposed sheet information output apparatus for gaining information as to a sheet material such as a paper sheet or a resin sheet by applying external force to the sheet material to detect a pressing force (impact force) through the sheet material.
Japanese Patent Application Laid-Open No. H05-095447 discloses a sheet information output apparatus for metering a deflection quantity of a sheet material to distinguish the deflection stiffness thereof. In this apparatus, the sheet material is conveyed while both edges of the sheet material are held by conveying rollers and passed through a displacement gauge as it is, so as to detect the stiffness.
Japanese Patent Application Laid-Open No. 2004-026486 discloses a sheet information output apparatus for gaining physical information as to a sheet material such as a paper sheet or a resin sheet by applying external force (percussion) to the sheet material to detect a pressing force (impact force) through the sheet material. In this apparatus, an application member is arranged in opposition to a receiving member in which a shallow depression has been formed, and the application member caused to strike on the surface of the sheet material supported over the shallow depression. When the application member is impacted on the sheet material aerially supported by the edge of the depression, the sheet material is deflection-deformed and then received by the bottom face of the depression and compression-deformed. A piezoelectric sensor for detecting impact force is arranged in the receiving member, and physical information as to the sheet material is distinguished on the basis of output from the piezoelectric sensor.
In the sheet information output apparatus disclosed in Japanese Patent Application Laid-Open No. H05-095447, a displacement quantity of the sheet itself due to curling or deformation is added as an error, and waving or fluttering of the sheet during its conveyance becomes an error, so that a deflection quantity based on the stiffness of the sheet cannot be successfully separated, and so an error in distinguishing of the stiffness of the sheet becomes great.
In the sheet information output apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-026486, excessive bending is given to a sheet depending on the combination of the forms and sizes in the grooved portion and the application member to increase an error in the detection of resistance force of deflective deformation, so that there is a possibility that an error in distinguishing of the stiffness of the sheet may become great. In addition, excessive shearing force or frictional force is caused to act on the sheet according to the form of the grooved portion, so that there is a possibility that the sheet may be damaged, which is, for example, locally deforming the sheet, leaving scratch on the surface thereof or creasing the sheet.
It is an object of the present invention to provide a sheet information output apparatus, by which a detection error of sheet information becomes little, little burden is imposed on a sheet to hardly damage the sheet.
Another object of the present invention is to provide a sheet information output apparatus, by which detection accuracy is not lowered even when a receiving member is changed with time by abrasion or the like.